1. INTRODUCTIONTop
1.1. The identity of stress and accent
The terms stress and accent have often been confoundedly used, referring to the same thing some times and to different things other times. In this study I take the position that they are different concepts, and look into their—also different—respective cues. The term stress is used to denote word-level prominence, i.e., metrical prominence assigned to a specific syllable in a certain word. This type of prominence is generally referred to as lexical stress. Definitions of lexical stress yet vary and their differentiations usually rely on the correlates assigned to it. Lehiste (1970) considers lexical stress an abstract property of the word that operates only when the word is placed in a context. Sluijter & Van Heuven (1996) abide by this definition of lexical stress as the non-figurative part of a word’s identity that has no phonetic entity of its own and define it as “a structural linguistic property of a word that specifies which syllable in the word is the strongest” (p. 2471). Stress for them is an abstract property of a word that serves as an index to the syllable within the word that has a potential to receive a pitch accent. Therefore, it is an abstract linguistic representation whose phonetic properties come in the foreground only when an accent is realized with it. Lexically stressed syllables are considered to always have an accent lending pitch movement associated with them when they occur within a single word produced in narrow focus (Sluijter, 1995). Stress, thus, is decided by language system rather than language behavior.
The term accent, however, is used to denote this phrasal-level prominence where one or more words within an utterance are chosen and assigned intonational prominence in addition to metrical prominence. This kind of prominence is a property of the utterance that is present in most languages of the world as it provides a means for the speaker to express communicational intentions and to organize speech. For various communicative purposes, one can increase one’s pitch range and project one’s voice to highlight new or important information in a particular sentence or phrase. This highlighted piece of information is said to receive a phrasal stress or an accent. However, each language following its own phonological system may vary as to the cues used to signal phrasal stress.
Phonetic correlates of phrasal stress other than f0 include duration, intensity, spectral balance, and vowel quality. Duration seems to be the second most important perceptual cue to phrasal stress after a change in f0. Phrasal stress has been reported to be responsible for changing the temporal pattern of words resulting in the lengthening of a constituent within the word, whether this is the stressed vowel, syllable or a larger domain (Beckman, Edwards & Fletcher, 1992; Turk & Sawusch, 1997; Turk & White, 1999). In addition, phrasal stress is correlated with an increase in intensity of the speech signal as well as a more smooth spectral tilt that could be explained by the increased pulmonary activity and vocalic effort made to produce phrasal stress. Intensity was considered to play an important role as a cue to phrasal stress. However, the cue of spectral tilt was suggested as a competitor to duration in signaling lexical and phrasal stress diminishing, thus, the importance of intensity, while vowel quality was considered an overall weaker cue to phrasal stress (Sluijter, 1995; Sluijter, Shattuck-Hufnagel, Stevens, & Van Heuven, 1995).
Summarizing the identity of phrasal stress and the way it is realized, we can plainly state that when a speaker produces a word or a phrase that includes new or important information, s/he may anticipate the additional effort the listener needs to incorporate it into memory. S/he realizes this word or phrase as being communicatively important by placing the word under focus (Baart, 1987; Ladd, 1980). This focused constituent is realized by placing a pitch accent on the prosodic head of the word or phrase. The prosodic head within the word is generally the lexically stressed syllable. In addition, the speaker may produce a slower speech rate and pronounce the focused word more carefully. This helps the listener to decide where s/he has to pay special attention. The acoustic correlates associated with such kind of prominence are expected to be more or less different from those of unfocused constituents.
1.2. Stress and accent in Arabic
Lexical stress placement in Arabic varies from standard to dialect and from one dialect to another but is in all cases fixed stress conditioned by syllabic weight. De Jong and Zawaydeh (1999) examined vowel durations, qualities, and f0 patterns of speakers of Arabic from Amman, Jordan. Lexical stress is reported to consistently affect duration and the F1 of low vowels. In fact, stress was found to interact with quantity in such a way to expand the already clear distinction between short and long vowels in Ammani Arabic. Surprisingly, there was no main effect of lexical focus on duration since it did not induce any lengthening, nor did it increase durational differences due to quantity. These findings confirm previous research on Arabic (Rajouani, Najim, Chiadmi, & Zyoute, 1987; Braham, 1997) which also found that duration is a very weak cue to stress in Modern Standard Arabic (MSA). Rajouani et al. (1987) studied the effects of intensity, pitch and duration on the perception of word stress in MSA produced by Moroccan speakers and found that the most important cue is pitch followed by intensity, and that the least important cue is duration. Braham (1997) reports no effects of stress on the duration of short vowels in MSA produced by Tunisian speakers. Duration is ranked last in this study, while the most important cue to stress was f0. Other research on the factors that affect syllabic structure in MSA (Ben Slama, 2002) also showed that there was no effect of stress on the duration of vowels in both normal and rapid speech. Braham (1997) explained the weakness of duration as correlate of stress in MSA by stating that Arabic is a language with a phonemic length contrast which has to be maintained even under stress so that no confusion is made between intrinsically long vowels and those lengthened by stress. However, in none of these studies a distinction between lexical and phrasal stress was made, which leads to confound their correlates.
This study tries to find out whether duration, vowel quality and spectral balance are correlates of stress and accent independently in two typologically different languages: Southern British English (SBE) and Tunisian Arabic (TA). The reasons are, first, to allow for a cross-linguistic comparison between the cues used to signal stress and accent in typologically distant languages, and, second, to deeply understand the phonic features of English since it is currently being taught as an important foreign language in Tunisia. The similarities or differences in the use of stress and accent are expected to affect the production of English word stress and accent by speakers of Tunisian Arabic and would hopefully provide more insight into the production and perception of L2 English prosodic features.
2. METHODOLOGYTop
2.1. Experiment 1: Measuring the acoustic correlates of stress and accent in SBE
2.1.1. Test material
The test material in this experiment comprised two sets of 12 disyllabic English minimal pairs of the kind ˈpermit ~ perˈmit which differ only in their stress pattern. The use of minimal pairs allows investigating the factor stress while other factors are kept constant. Thus, acoustic measures made on the first syllable of ˈpermit (noun) are compared to the same measures made on the first syllable of perˈmit (verb). The word pairs were placed in focused and non-focused conditions in order to assess the impact that focus may have over stress and the interaction between them. The frame sentences where the target words are placed were the same. They were designed to naturally elicit from the speakers the desired prosodic contour, and in order to aid in segmentation. Two contexts of the same carrier sentence were contrasted, one which directed phrasal stress on the target word, and one which deviated phrasal stress from the target word. The way to signal which word was prominent each time was to write it in bold capital letters. The position of the target word in the two focus conditions was non-final to eliminate any effects of constituent final lengthening. The content of the frame sentences was such that it depicted a semantic relationship between the target word in the experimental sentence and a foil word in the sentence before. This was meant to aid the speakers in giving prominence to the desired word for the purpose of the experiment. Besides, the subjects had the category of the word marked on the cards they read to know where to place lexical stress. Examples are provided in (1).
- (1) [+Focus] condition: Lexical stress + phrasal stress
Say LICENCE again.
Say PERMIT again.
Since this is a command and since there is a semantic relationship between the two words in bold, the target syllable in permit for example will be both lexically and phrasally stressed. It is focused because it is contrasted to licence in the sentence before and the pitch accent therefore falls on it. The example in (2), however, illustrates the condition where lexical stress is measured independently of focus.
- (2) [−Focus] condition: Lexical stress only (phrasal stress is placed on the word in bold)
A permit is another word for licence.
WRITE permit again.
SAY permit again.
Here a pre-cursor sentence is used to suggest the likely location of new or unpredictable information on the assumption that unpredictable words are likely to bear phrasal stress. In this example, phrasal stress is placed on write and say as opposed to each other and as being the new information in this case. Focus is therefore deviated from the target word permit, hence the target syllable per will be analyzed as merely lexically stressed with no focus being placed on it at the same time. The terms [+Focus], [−Focus] and their abbreviations [+F] and [−F] are used to indicate the focus condition, while the abbreviations [+S] and [−S] refer to stressed and unstressed targets (vowels or syllables). In order to ensure that the findings can be generalized, twelve minimal pairs were used as test words in each experimental condition. The subjects were instructed to produce the desired lexical and phrasal stress in the right focus conditions.
2.1.2. Subjects
The subjects for this study were six speakers (5 males and 1 female) of British English with a southern accent and with no known hearing or speaking disorders. They were between the age of 26 and 55 and voluntarily accepted to be recorded.
2.1.3. Recording procedure
Recordings took place in one of the recording studios in the Department of Theoretical and Applied Linguistics, University of Edinburgh. They were made in a soundproof room using an AKG hypercardiod microphone and downsampled to 16 kHz mono. In the recording session, speakers initially read five sentences for practice randomly selected from the experimental sentences and other sentences. They were presented to the subjects in two blocks of 24 each, one block of nouns (initial stress) and one block of verbs (final stress) composed of the 24 experimental sentences and 24 other filler sentences placed in a random order.
Subjects were instructed to read the sentences with a normal speech rate, not to pause between words and to focus the words written in bold capital letters. They read the cards presented to them three times. After each repetition, cards were shuffled to get randomized again. The subjects were asked to repeat sentences that were incorrectly uttered.
2.1.4. Data collected
The data comprised 24 test words in two focus conditions, [+F] and [−F], pronounced three times by 6 native speakers of English. The result was 24 (words) * 2 (focus conditions) * 6 (speakers) * 3 (repetitions) = 864 words. The wrong utterances omitted were 53, giving 811 utterances to segment and analyze.
2.2. Experiment 2: Measuring the acoustic correlates of stress and accent in Tunisian Arabic
2.2.1. Test material
Two sets of 10 disyllabic Tunisian Arabic near minimal pairs of the kind: /ˈbeddel/ ~ /bedˈdelt/ were used. The choice of these near minimal pairs is meant to allow investigating the effect of stress in the same consonantal environment. Thus, the acoustic measurements made on the first syllable of /ˈbeddel/ ‘he changed’ are compared with the same measures made on the first syllable of /bedˈdelt/ ‘I changed’. The word pairs were also placed in a focused and a non-focused condition in order to assess the impact that focus may have over stress and the interaction between them. The frame sentences in which the target words were placed were the same, designed to naturally elicit from the speakers the desired prosodic contour and aid in segmentation. Two contexts of the same carrier sentence were also contrasted, one which directed phrasal stress on the target word and one which deviated phrasal stress from it. The way to signal which word was prominent each time was writing it in bold bigger letters in Arabic script. The position of the target word in the two focus conditions was again non-final for the same purposes mentioned in experiment 1. The content of the frame sentences was such that it depicted a semantic relationship between the target word in the experimental sentence and a filler word in the previous sentence. When no semantic relationship between the words could be found, a word that rimes with the test word was chosen instead. This was meant to aid the speakers in giving prominence to the desired word. Examples are provided in (3).
- (3) [+Focus] condition: Lexical stress + phrasal stress
/ԛul ˈχɑmmɑm mɑrtin/
/ԛul ˈfɑkkɑr mɑrtin/
Translation:
‘Say consider twice’
‘Say think twice’
Since this is a command and since there is a semantic relationship between the two words in bold (synonyms), the target syllable (underlined) in the target word (/ˈfɑkkɑr/ in this example) will be both lexically and phrasally stressed. It is focused because it is related to /ˈχɑmmɑm/ in the sentence before and the pitch accent, therefore, falls on it. The example below, however, illustrates the condition where lexical stress is measured independently of focus in experiment 2.
- (4) [−Focus] condition: Lexical stress only (phrasal stress is placed on the word in bold)
/ˈfɑkkɑr kɪlmә sәhlә/
/ԛul ˈfɑkkɑr mɑrtin/
/ʢɑwɪd ˈfɑkkɑr mɑrtin/
Translation:
‘Think is an easy word’
‘SAY think twice’
‘REPEAT think twice’
A precursor sentence is used to suggest the likely location of new or unpredictable information. In this example, phrasal stress is placed on /ԛul/ and /ˈʢɑwɪd/ as opposed to each other and as being the new information in this context. Focus is, therefore, deviated from the target word /ˈfɑkkɑr/, and the target syllable /fɑk/ will be analyzed as being lexically stressed only, with no focus, hence, no pitch accent placed on it. Ten near minimal pairs were used in each experimental condition.
2.2.2. Subjects
Six Tunisian students were recorded. They were all native speakers of Tunisian Arabic with no hearing or speaking disorders. They were three females and three males between the age of 22 and 26 majoring in English.
2.2.3. Recording procedure
Recordings took place in a soundproof room using a professional microphone. They were recorded directly onto a computer at a frequency response of 44.1 kHz and then downsampled to 16 kHz mono. The subjects had two training sessions with the author to get familiar with the test words. Parallel procedures were followed in that in the recording session the subjects initially read five sentences for practice selected randomly from the experimental sentences and other sentences. They were presented to the subjects in two blocks of 20 each composed of the 20 experimental sentences and 20 other foil sentences put in a random order (one block for the items that receive an initial stress, and one block for the items that receive a final stress). Subjects were instructed to emphasize the words written in bold, not to pause between words, and to keep a normal pace in their speech. The subjects read the cards presented to them three times for each block of cards after being shuffled each time.
2.2.4. Data collected
The data comprised 20 (words) * 2 (focus conditions) * 6 (speakers) * 3 (repetitions) = 720 words to be segmented and analyzed.
2.3. Segmentation criteria
The segmentation criteria were based on the spectral characteristics most identifiable in spectrograms with the aid of waveform displays that are helpful in showing dips and rises in amplitude often corresponding to onsets of constrictions and their releases. The corpus was comprised of various classes of sounds including oral stops, fricatives, and nasal stops. As onsets and releases of oral consonantal constrictions producing stops, fricatives and affricates often coincide with abrupt spectral changes (Turk, Nakai & Sugahara, 2006) acoustic segment durations were determined by the intervals that these oral consonantal events define. The duration of a vowel is defined as the duration of the interval between a C1 constriction release landmark and a following C2 constriction onset landmark in a C1VC2 sequence. This interval is, however, not totally vocalic as it includes formant transitions and noise burst that cue the identity of surrounding consonants in addition to any aspiration from preceding voiceless aspirated stops. For geminate consonants in the Arabic data, a temporal midpoint was hypothesized to be taken as the end of one portion of the sound and the beginning of its next portion.
2.4. Data Analysis
Records of segmentation decisions were kept for each audio file via the use of associated label files. Special Praat scripts were then used for automatic measurements of the dependent variables, mainly duration, F1, F2 and spectral balance. Measurements of different variables were extracted through the aid of these scripts in a format that can be used in spreadsheets. Measures of f0 at the midpoint of the target vowel and of intensity at the peak of the target vowel were obtained by hand, but their results are not reported here because they need further refinement. Statistical analysis of the values obtained was performed through SPSS, version 15.
3. RESULTSTop
3.1. Experiment 1: The acoustic correlates of stress and accent in SBE
3.1.1. Duration
Duration measurements taken from the disyllabic test words are obtained for both initial and final stressed and unstressed syllables in the two focus conditions ([+F] and [−F]). The aim from this is to examine the effects that stress, focus and syllable position (initial vs. final) have on duration in SBE, as well as the interaction between these factors.
The mean length differences between initial stressed and unstressed syllables in the [+F] context show that, when a pitch accent is realized on the word, the duration of stressed syllables in SBE exceeds that of unstressed syllables by almost 37 %. However, when no pitch accent is realized on the word, that is, in the [−F] context, a mean length difference of almost 50 ms is found between initial stressed and unstressed English syllables, representing about 23 % length difference. To check the significance of the values obtained, the duration values of the initial syllable were subjected to a two-way repeated measure ANOVA with stress [+S, −S] and focus [+F, −F] as fixed effects, repetition as a repeated measure, and subject as a random factor. Results show that factor stress was significant (F (1, 5) = 64.3; p < .001), focus was also significant (F (1, 5) = 96.04; p < .001), while the interaction between stress and focus was non-significant. This shows that duration is a correlate of lexical stress in SBE, that is, when the target syllable is not placed under focus, and that duration is a correlate of accent (phrasal stress) as well, since focus is found to have a significant effect on duration in the [+F] condition, namely, when the target syllable is placed under focus and receives the pitch accent.
The effect of phrasal stress on the duration of both stressed and unstressed syllables in both initial and final positions was then examined. The values obtained show a mean length difference of about 26 ms between initial stressed English syllables in the [+F] and [−F] contexts. Focus seems to augment the duration of the initial stressed syllable. To explore the interaction between syllable position and focus effects, the final stressed syllable of the disyllabic test words was also measured and the way it is affected by focus was assessed. The duration values obtained show that all the six speakers produce longer duration when they place the word under focus. A mean length difference of almost 45 ms is found between the two focus conditions, representing 13 % of lengthening. Focus, apparently, has in SBE a significant lengthening effect on the duration of final stressed syllables as well.
In order to check the statistical significance of the focus effect on duration of stressed syllables and to assess any possible interaction between focus and syllable position for stressed syllables in English, a two-way ANOVA is used with focus and syllable position as fixed effects, repetition as a repeated measure, and with subject as a random factor. As expected from the mean values obtained, the factor focus is found to be highly significant (F (1, 5) = 61.78; p < .001), syllable position is also highly significant (F (1, 5) = 56.18; p < .001) but the interaction between them is non-significant, which shows that focus increases the duration of the stressed syllable in SBE disyllabic words whether in initial or final position.
The effect of phrasal stress on the duration of unstressed syllables, both initial and final, was then examined to find out whether focus lengthens the duration of unstressed syllables in SBE. Comparing the mean duration of initial unstressed syllables [+F] and [−F], a small length difference of about 10 ms is found. For unstressed final syllables [+F] and [−F], the values show that all speakers produced longer duration when a pitch accent is used. The length difference between the focus contexts is of about 26 ms. Focus seems to lengthen the duration of the final unstressed syllable in English. Since previous literature on English (Turk & White, 1997; Turk & Sawusch, 1999) leads us to expect an interaction between focus-related lengthening and syllable position for unstressed syllables, a two-way ANOVA with focus and syllable position as fixed effects, repetition as a repeated measure and subject as a random factor is used for unstressed syllables. Results revealed that syllable position is highly significant (F (1, 5) = 88.05; p < .001). The factor focus is also significant (F (1, 5) = 14.47; p < .001). However, contrary to stressed syllables, a significant interaction is found between syllable position and focus for unstressed syllables (F (1, 5) = 10.72; p < .05). Focus seems to lengthen the duration of final unstressed syllables only in SBE. Figure 1 illustrates these results.
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Figure 1. Effects of focus on duration (in ms) of stressed and unstressed syllables in initial and final positions by six speakers of SBE. |
3.1.2. Spectral Balance Results for SBE
Results for two measures of spectral balance H1−A3 and H1−A2 are presented for SBE. H1 and H2 refer to the amplitudes of the first and second harmonics, respectively, while A2 and A3 refer to the amplitudes of F2 (second formant) and F3 (third formant), respectively. Unstressed vowels are expected to have less energy at higher frequencies, hence higher values for H1−A2 and H1−A3. These two measures were investigated for both lexical stress positions (stressed and unstressed) and in both focus conditions for four vowels produced by 5 male native English speakers. The vowels from which the tilt measures are taken are all the monophthongs occurring in the first syllable of the minimal pairs test words. They include /ɒ/ in pairs like ˈcontract ~ conˈtract, /e/ in ˈrecord ~ reˈcord, /ɜ/ in ˈpermit ~ perˈmit, and /ʌ/ in ˈsubject ~ subˈject. The /ɒ/ in the pair ˈobject ~ obˈject was discarded from the vowel analysis because it occurs word-initially and was often glottalized by most of the informants and glottalization is known to independently affect spectral balance.
The effect of stress is first investigated on the H1−A3 measure of spectral balance in the presence of focus, i.e. in the [+F] condition, on the target word. Table 1 presents the mean values and standard deviations for this tilt measure of glottal closure, and skewness of the glottal pulse of stressed and unstressed four English vowels in the [+F] context.
Table 1: St deviation and mean values of H1−A3 for four English vowels by five male speakers in the [+F] and the [−F] contexts.
| Vowels | Mean H1−A3 (in dB) | Mean H1−A3 (in dB) | ||||
|---|---|---|---|---|---|---|
| [−S, +F] | [+S, +F] | St deviation | [−S, −F] | [+S,−F] | St Deviation | |
| /ɜ/ | 16.50 | 8.50 | 2.33 | 26.15 | 20.30 | .66 |
| /e/ | 25.10 | 17.95 | 1.89 | 29.85 | 23.90 | 1.45 |
| /ɒ/ | 26.20 | 15.20 | 2.86 | 28.90 | 21.15 | 2.06 |
| /ʌ/ | 26.40 | 17.20 | 1.93 | 30.30 | 20.9 | 2.33 |
As shown in Table 1, unstressed vowels had higher H1−A3 values indicating a more high frequency emphasis for stressed vowels. In the [−F] context too, unstressed vowels have higher H1−A3 values. To check the significance of these values, a three-way fixed effect ANOVA is used with vowel type, stress, and focus as fixed factors, repetition as a repeated measure, and speaker as random factor. The factor vowel type is found to be non-significant (F (3, 288) = .32; p > .05). This shows that H1−A3 is not significantly different for these vowels. The effect of stress on this tilt measure is, however, found to be highly significant (F (1, 288) = 54.42; p < .001).
Focus is also found to be highly significant (F (1, 288) = 74.33; p < .001). No significant interaction is found between vowel type and stress or between vowel type and focus. A tendency towards significance is found for the interaction between stress and focus (F (1, 288) = 5.33; p > .05 (p = .069)). The three-way interaction between vowel type, stress, and focus is non-significant.
The effect of stress was then investigated on the H1−A2 measure of spectral balance in the presence of focus on the target word (see Table 2).
Table 2: St deviation and mean values of H1−A2 for four English vowels by five male speakers in the [+F] and [−F] contexts.
| Vowels | Mean H1−A2 + 10 (in dB) [1] | Mean H1−A2 + 10 (in dB) | ||||
|---|---|---|---|---|---|---|
| [−S, +F] | [+S, +F] | St Deviation | [−S, −F] | [+S, −F] | St Deviation | |
| /ɜ/ | 15.33 | 8.35 | 2.94 | 18.50 | 12.80 | 2.75 |
| /e/ | 18.24 | 7.95 | 3.61 | 18.35 | 12.10 | 2.15 |
| /ɒ/ | 18.98 | 9.45 | 3.05 | 21.70 | 14.85 | 2.25 |
| /ʌ/ | 20.36 | 4.55 | 6.33 | 23.15 | 10.80 | 3.65 |
[1] Note that the H1-A2 values are offset by 10dB to adjust the negative values.
Table 2 presents mean values and standard deviations for H1−A2 as a measure of glottal closure and skewness of the glottal pulse for 4 stressed and unstressed English vowels in the [+F] context. It is clear from the table that unstressed vowels have higher H1−A2 values, indicating a more high frequency emphasis for stressed vowels. Unstressed vowels in the [−F] context also had H1−A2 values almost twice as high as the values of stressed vowels especially for /ʌ/.
Just like for the H1−A3 measure, a three-way analysis of variance is used to check the significance of the results and see whether there is any significant interaction between the factors vowel type, stress, and focus. The effect of vowel type is found to be non-significant, which shows that H1−A2 is not significantly different for these different vowels. This is probably because the vowels chosen are not very distant in the vocalic space. The effect of stress is highly significant (F (1, 288) = 164.57; p < .001). Results showed a significant effect of focus, too (F (1, 288) = 65.57; p < .001). No significant interaction is found between vowel type and stress or between vowel type and focus. A very significant interaction is however found between stress and focus (F (1, 288) = 13.40; p < .001). The significant interaction found between stress and focus in the H1−A2 measure shows that the magnitude of the stress effect depends on the focus value as there is a greater effect of stress on focused constituents. It also shows that the effect of focus depends on the stress value. It is more pronounced for stressed vowels. The three-way interaction between stress, focus and vowel type is, however, non-significant.
Summarizing the results of experiment 1 on spectral balance as a correlate of stress and/or accent in SBE, we find that both measures, H1−A2 and H1−A3, are reliable measures of spectral tilt. In both focus conditions, unstressed syllables have higher H1−A2 and H1−A3 values indicating higher frequency emphasis for stressed vowels. The factors stress and focus are both found to have significant effects on these measures of spectral balance, while vowel type effect is non-significant. Spectral balance can accordingly be considered a correlate of both lexical and phrasal stress in SBE.
3.1.3. Vowel quality results for SBE
The data analyzed are those of the five male speakers only. The female speaker was discarded from the analysis because sex is known to affect the formant values of vowels and one female speaker only does not make it possible to include the variable sex in the analysis. The formant values (F1 and F2) are calculated at a midpoint of the vowel segment specified in a text grid. The procedure is repeated automatically through a script, but values were also manually checked.
The vowels measured are those existing in the disyllabic minimal pair test words except the diphthong in digest to allow for a more homogenous comparison between the rest of the monophthong vowels, /ɒ/ /e/, /ɜ/ and /ʌ/.
Formant values F1 and F2 are measured in stressed and unstressed position in both focus conditions. The values obtained are compared and tested for significance through fixed-effect ANOVA tests. A three-way ANOVA was performed on each formant separately with vowel type, stress, and focus as fixed effects, repetition as a repeated measure and speaker as a random factor. The results for F1 show that the vowel type and focus have a non significant effect. On the contrary, the effect of stress on F1 is highly significant (F (1, 240) = 44.02; p < .001). No two-way interaction is at all found between vowel and stress, vowel and focus, or between stress and focus. The three-way interaction between stress, vowel, and focus is also non-significant. The F1 of these British English vowels seems, thus, to be affected by lexical stress only, and not by focus accent.
The results for F2 show that the vowel type effect is highly significant (F (3, 240) = 32.34; p < .001). Focus had no significant effect on F2. Stress also had no significant effect. The effect of the factor stress can be, however, seen in the significant interaction existing between vowel type and stress (F (3, 240) = 14.32; p < .001), which indicates that the magnitude of the stress effect on F2 depends on vowel type. The interaction between vowel and focus is non-significant. The interaction between stress and focus is non-significant, too. The three-way interaction between stress vowel and focus is also non-significant. The results of experiment 1 on vowel quality as a correlate of stress and accent in SBE show that F1 in these British English vowels is affected by stress only. Focus does not affect it at all. Focus does not affect F2, either. Stress, nevertheless, seems to have an effect on F2 as shown in the significant interaction existing between vowel type and stress. This interaction shows that the stress effect on F2 depends on the type of the vowel in SBE. Figures 2 and 3 show the results of the variables stress, focus and vowel on each formant separately.
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Figure 2. Effects of vowel type, stress, and focus on F1 (in Hz) in four English vowels by five male speakers. |
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Figure 3. The effects of vowel type, stress, and focus on F2 (in Hz) in four English vowels. |